Advances in the development and improvements of the luminous flux of light-emitting devices such as solid-state semiconductor and organic light-emitting diodes (LEDs) have made these devices suitable for use in general illumination applications, including architectural, entertainment, and roadway lighting. Light-emitting diodes are becoming increasingly competitive with light sources such as incandescent, fluorescent, and high-intensity discharge lamps.
In particular, some general-purpose LED-based light sources have been proposed to provide a good color rendering performance comparable with currently used general-purpose light sources. For instance, certain types of phosphor-coated LEDs (pc LEDs) have been developed to provide a reasonably good white light source, wherein emissions from the LED induce, and sometimes combines with, emissions from the phosphorous coating to produce the white light.
Other LED-based light sources are generally disclosed to provide white light by combining the emissions of at least three LEDs, the wavelengths of which being specifically selected to optimise the color rendering index (CRI) of the disclosed light source. For instance, in U.S. Pat. No. 5,851,063 for a Light-Emitting Diode White Light Source, issued Dec. 22, 1998 to Doughty et al., a system of at least three multicolored LEDs is disclosed to have an optimised CRI by proper selection of the wavelengths of each LED. The disclosed system is said to be useful for general illumination purposes due to its optimised CRI. In U.S. Pat. Nos. 7,008,078 and 6,817,735, a light source is disclosed to include four different types of LEDs, namely a blue LED, a blue-green LED, an orange LED and a red LED, each respectively emitting light within a predefined range of wavelengths selected to provide a high efficiency and a high color rendering performance.
Further LED-based light sources have been disclosed to comprise a feedback system enabling such light sources to adjust an output of the light-source's LEDs as a function of a feedback signal in order to substantially maintain a desired output. For example, feedback signals related to light source output color, intensity or operating temperature are used to adjust an output of the light source to substantially maintain a pre-set operating condition. Examples of such light sources are provided in U.S. Pat. No. 6,411,046, United States Patent Application Nos. 2005/0237733, 2005/0161586 and 2004/0211888, and International Application Nos. WO 2004/025998 and WO 2004/100611.
Some challenges, however, still need to be resolved to adapt current and upcoming LED technology to general illumination applications. For instance, in order to make general purpose LED-based light sources competitive with, and ultimately surpass, currently available general purpose light sources, techniques must be developed to improve and preferably optimise the general illumination characteristics of such LED-based devices via optimised drive parameters. Namely, though LED-based technologies have been disclosed to optimise the CRI of LED-based light sources by selecting specific LED wavelengths conducive to such optimisation, these wavelength optimisation techniques are generally only applicable for a prescribed correlated color temperature (CCT) and, in practice, can raise cost issues associated with the sort of binning required for the manufacture of these optimised light sources. As such, there is a need for light source solutions using currently available LEDs and/or other such light emitting elements, or again using newly developed light-emitting elements, which can not only improve and/or optimise the CRI of such light sources, but also optionally improve and/or optimise for other selected illumination characteristics of such devices, such as, for example, the color quality scale (CQS), the luminous efficacy and/or the output power.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.